What would be the best approach to reverse a large text file that is uploaded asynchronously to a servlet that reverses this file in a scalable and efficient way?

• text file can be massive (gigabytes long)
• can assume mulitple server/clustered environment to do this in a distributed manner.
• open source libraries are encouraged to consider

I was thinking of using Java NIO to treat file as an array on disk (so that I don't have to treat the file as a string buffer in memory). Also, I am thinking of using MapReduce to break up the file and process it in separate machines.

Any input is appreciated. Thanks.

• Daniel